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S_CLIENT(1)			    OpenSSL			   S_CLIENT(1)

       openssl-s_client, s_client - SSL/TLS client program

       openssl s_client	[-connect host:port] [-servername name]	[-verify
       depth] [-verify_return_error] [-cert filename] [-certform DER|PEM]
       [-key filename] [-keyform DER|PEM] [-pass arg] [-CApath directory]
       [-CAfile	filename] [-no_alt_chains] [-reconnect]	[-pause] [-showcerts]
       [-debug]	[-msg] [-nbio_test] [-state] [-nbio] [-crlf] [-ign_eof]
       [-no_ign_eof] [-quiet] [-ssl2] [-ssl3] [-tls1] [-no_ssl2] [-no_ssl3]
       [-no_tls1] [-no_tls1_1] [-no_tls1_2] [-fallback_scsv] [-bugs] [-sigalgs
       sigalglist] [-curves curvelist] [-cipher	cipherlist] [-serverpref]
       [-starttls protocol] [-engine id] [-tlsextdebug]	[-no_ticket]
       [-sess_out filename] [-sess_in filename]	[-rand file(s)]	[-serverinfo
       types] [-status]	[-alpn protocols] [-nextprotoneg protocols]

       The s_client command implements a generic SSL/TLS client	which connects
       to a remote host	using SSL/TLS. It is a very useful diagnostic tool for
       SSL servers.

       -connect	host:port
	   This	specifies the host and optional	port to	connect	to. If not
	   specified then an attempt is	made to	connect	to the local host on
	   port	4433.

       -servername name
	   Set the TLS SNI (Server Name	Indication) extension in the
	   ClientHello message.

       -cert certname
	   The certificate to use, if one is requested by the server. The
	   default is not to use a certificate.

       -certform format
	   The certificate format to use: DER or PEM. PEM is the default.

       -key keyfile
	   The private key to use. If not specified then the certificate file
	   will	be used.

       -keyform	format
	   The private format to use: DER or PEM. PEM is the default.

       -pass arg
	   the private key password source. For	more information about the
	   format of arg see the PASS PHRASE ARGUMENTS section in openssl(1).

       -verify depth
	   The verify depth to use. This specifies the maximum length of the
	   server certificate chain and	turns on server	certificate
	   verification.  Currently the	verify operation continues after
	   errors so all the problems with a certificate chain can be seen. As
	   a side effect the connection	will never fail	due to a server
	   certificate verify failure.

	   Return verification errors instead of continuing. This will
	   typically abort the handshake with a	fatal error.

       -CApath directory
	   The directory to use	for server certificate verification. This
	   directory must be in	"hash format", see verify for more
	   information.	These are also used when building the client
	   certificate chain.

       -CAfile file
	   A file containing trusted certificates to use during	server
	   authentication and to use when attempting to	build the client
	   certificate chain.

       -purpose, -ignore_critical, -issuer_checks, -crl_check, -crl_check_all,
       -policy_check, -extended_crl, -x509_strict, -policy -check_ss_sig
	   Set various certificate chain valiadition option. See the verify
	   manual page for details.

	   reconnects to the same server 5 times using the same	session	ID,
	   this	can be used as a test that session caching is working.

	   pauses 1 second between each	read and write call.

	   display the whole server certificate	chain: normally	only the
	   server certificate itself is	displayed.

	   print session information when the program exits. This will always
	   attempt to print out	information even if the	connection fails.
	   Normally information	will only be printed out once if the
	   connection succeeds.	This option is useful because the cipher in
	   use may be renegotiated or the connection may fail because a	client
	   certificate is required or is requested only	after an attempt is
	   made	to access a certain URL. Note: the output produced by this
	   option is not always	accurate because a connection might never have
	   been	established.

	   prints out the SSL session states.

	   print extensive debugging information including a hex dump of all

	   show	all protocol messages with hex dump.

	   tests non-blocking I/O

	   turns on non-blocking I/O

	   this	option translated a line feed from the terminal	into CR+LF as
	   required by some servers.

	   inhibit shutting down the connection	when end of file is reached in
	   the input.

	   inhibit printing of session and certificate information.  This
	   implicitly turns on -ign_eof	as well.

	   shut	down the connection when end of	file is	reached	in the input.
	   Can be used to override the implicit	-ign_eof after -quiet.

       -psk_identity identity
	   Use the PSK identity	identity when using a PSK cipher suite.	 The
	   default value is "Client_identity" (without the quotes).

       -psk key
	   Use the PSK key key when using a PSK	cipher suite. The key is given
	   as a	hexadecimal number without leading 0x, for example -psk
	   1a2b3c4d.  This option must be provided in order to use a PSK

       -ssl2, -ssl3, -tls1, -tls1_1, -tls1_2, -no_ssl2,	-no_ssl3, -no_tls1,
       -no_tls1_1, -no_tls1_2
	   These options require or disable the	use of the specified SSL or
	   TLS protocols.  By default the initial handshake uses a version-
	   flexible method which will negotiate	the highest mutually supported
	   protocol version.

	   Send	TLS_FALLBACK_SCSV in the ClientHello.

	   there are several known bug in SSL and TLS implementations. Adding
	   this	option enables various workarounds.

       -sigalgs	sigalglist
	   Specifies the list of signature algorithms that are sent by the
	   client.  The	server selects one entry in the	list based on its
	   preferences.	 For example strings, see SSL_CTX_set1_sigalgs(3)

       -curves curvelist
	   Specifies the list of supported curves to be	sent by	the client.
	   The curve is	is ultimately selected by the server. For a list of
	   all curves, use:

	       $ openssl ecparam -list_curves

       -cipher cipherlist
	   this	allows the cipher list sent by the client to be	modified.
	   Although the	server determines which	cipher suite is	used it	should
	   take	the first supported cipher in the list sent by the client. See
	   the ciphers command for more	information.

	   use the server's cipher preferences;	only used for SSLV2.

       -starttls protocol
	   send	the protocol-specific message(s) to switch to TLS for
	   communication.  protocol is a keyword for the intended protocol.
	   Currently, the only supported keywords are "smtp", "pop3", "imap",
	   "ftp" and "xmpp".

	   print out a hex dump	of any TLS extensions received from the

	   disable RFC4507bis session ticket support.

       -sess_out filename
	   output SSL session to filename

       -sess_in	sess.pem
	   load	SSL session from filename. The client will attempt to resume a
	   connection from this	session.

       -engine id
	   specifying an engine	(by its	unique id string) will cause s_client
	   to attempt to obtain	a functional reference to the specified
	   engine, thus	initialising it	if needed. The engine will then	be set
	   as the default for all available algorithms.

       -rand file(s)
	   a file or files containing random data used to seed the random
	   number generator, or	an EGD socket (see RAND_egd(3)).  Multiple
	   files can be	specified separated by a OS-dependent character.  The
	   separator is	; for MS-Windows, , for	OpenVMS, and : for all others.

       -serverinfo types
	   a list of comma-separated TLS Extension Types (numbers between 0
	   and 65535).	Each type will be sent as an empty ClientHello TLS
	   Extension.  The server's response (if any) will be encoded and
	   displayed as	a PEM file.

	   sends a certificate status request to the server (OCSP stapling).
	   The server response (if any)	is printed out.

       -alpn protocols,	-nextprotoneg protocols
	   these flags enable the Enable the Application-Layer Protocol
	   Negotiation or Next Protocol	Negotiation extension, respectively.
	   ALPN	is the IETF standard and replaces NPN.	The protocols list is
	   a comma-separated protocol names that the client should advertise
	   support for.	The list should	contain	most wanted protocols first.
	   Protocol names are printable	ASCII strings, for example "http/1.1"
	   or "spdy/3".	 Empty list of protocols is treated specially and will
	   cause the client to advertise support for the TLS extension but
	   disconnect just after reciving ServerHello with a list of server
	   supported protocols.

       If a connection is established with an SSL server then any data
       received	from the server	is displayed and any key presses will be sent
       to the server. When used	interactively (which means neither -quiet nor
       -ign_eof	have been given), the session will be renegotiated if the line
       begins with an R, and if	the line begins	with a Q or if end of file is
       reached,	the connection will be closed down.

       s_client	can be used to debug SSL servers. To connect to	an SSL HTTP
       server the command:

	openssl	s_client -connect servername:443

       would typically be used (https uses port	443). If the connection
       succeeds	then an	HTTP command can be given such as "GET /" to retrieve
       a web page.

       If the handshake	fails then there are several possible causes, if it is
       nothing obvious like no client certificate then the -bugs, -ssl2,
       -ssl3, -tls1, -no_ssl2, -no_ssl3, -no_tls1 options can be tried in case
       it is a buggy server. In	particular you should play with	these options
       before submitting a bug report to an OpenSSL mailing list.

       A frequent problem when attempting to get client	certificates working
       is that a web client complains it has no	certificates or	gives an empty
       list to choose from. This is normally because the server	is not sending
       the clients certificate authority in its	"acceptable CA list" when it
       requests	a certificate. By using	s_client the CA	list can be viewed and
       checked.	However	some servers only request client authentication	after
       a specific URL is requested. To obtain the list in this case it is
       necessary to use	the -prexit option and send an HTTP request for	an
       appropriate page.

       If a certificate	is specified on	the command line using the -cert
       option it will not be used unless the server specifically requests a
       client certificate. Therefor merely including a client certificate on
       the command line	is no guarantee	that the certificate works.

       If there	are problems verifying a server	certificate then the
       -showcerts option can be	used to	show the whole chain.

       Since the SSLv23	client hello cannot include compression	methods	or
       extensions these	will only be supported if its use is disabled, for
       example by using	the -no_sslv2 option.

       The s_client utility is a test tool and is designed to continue the
       handshake after any certificate verification errors. As a result	it
       will accept any certificate chain (trusted or not) sent by the peer.
       None test applications should not do this as it makes them vulnerable
       to a MITM attack. This behaviour	can be changed by with the
       -verify_return_error option: any	verify errors are then returned
       aborting	the handshake.

       Because this program has	a lot of options and also because some of the
       techniques used are rather old, the C source of s_client	is rather hard
       to read and not a model of how things should be done. A typical SSL
       client program would be much simpler.

       The -prexit option is a bit of a	hack. We should	really report
       information whenever a session is renegotiated.

       sess_id(1), s_server(1),	ciphers(1)

       The -no_alt_chains options was first added to OpenSSL 1.0.2b.

1.0.2o				  2018-03-27			   S_CLIENT(1)


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